An exposure apparatus is used, for example, for forming a wiring pattern etc. in a manufacturing process of a printed circuit board, a liquid crystal panel etc. (hereinafter referred to as a workpiece). FIG. 6 shows a configuration example of such an exposure apparatus. The exposure apparatus shown in FIG. 6 comprises a projection lens, and is a projection type exposure apparatus, in which a mask pattern is projected onto a workpiece by the projection lens to perform an exposure. In the projection type exposure apparatus shown in the figure, an alignment mark (hereinafter referred to as a work mark WAM) is formed on a back side face of the workpiece W, and the position of the alignment mark on the back side face of this workpiece and the position of an alignment mark formed on a mask M (hereinafter referred to as mask marks MAM) are aligned so that an exposure may be carried out. Such an exposure apparatus is disclosed in Japanese Patent No. 3201233. The exposure apparatus mainly comprises a light emitting unit 10, the mask M in which a pattern to be exposed (transferred) onto a workpiece is formed, a mask, stage 20, which holds the mask, a work stage 30 including an adsorption table 33, which holds the workpiece W to be exposed, such as a printed circuit board and a liquid crystal panel, and the projection lens 40, which projects the pattern, formed in the mask M, onto the workpiece W held on the adsorption table 33. In addition, there is also another type of exposure apparatus, which uses a mirror but does not use a lens as a projection means for projecting a pattern, which is formed in the mask M, onto the workpiece W, which is held on the work stage 30.
The light emission unit 10 includes a lamp 11, which is a light source for emitting exposure light, and a mirror 12, which reflects light emitted from the lamp 11, etc. Moreover, the work stage 30 comprises the adsorption table 33, which holds the workpiece W, a moving stage 32, which includes a XYθ drive unit 37, and a Z direction moving stage moving mechanism 50 including a Z drive unit 51, wherein the moving stage 32 is placed on the Z direction moving stage moving mechanism 50. Moreover, the adsorption table 33 holding the work W is attached to the moving stage 32. The moving stage 32 and the adsorption table 33 of the work stage 30 are moved by the XYθ drive unit 37 in XY directions (two axes, which are parallel to a workpiece face—a face that is irradiated with exposure light—and intersect with each other, that is, two axes, which intersect with the optical axis of a projection lens at right angles) and in a θ direction (rotation with respect to an axis that is perpendicular to the workpiece face, i.e., rotation with respect to the axis parallel to the optical axis L of the projection lens 40). In addition, the moving stage 32 and the adsorption table 33 of the work stage 30 are moved in a Z direction (a direction perpendicular to the workpiece face, that is, parallel to the optical axis L of the projection lens 40) by the Z drive unit 51 of the Z direction moving stage moving mechanism 50. The adsorption table 33 is also moved in the XYθ drive directions integrally with the moving stage 32.
A drive apparatus for the XYθ drive unit 37 is, for example, a radial type servo motor in which a detection unit (such as an encoder) for detecting the amount of movement thereof in the XYθ direction is built. The moving stage 32 is attached to the servo motor through a linear guide, ball screws, etc., wherein the moving stage 32 can be moved in the XYθ direction by driving the servo motor. Similarly, the Z drive unit 51 of the Z direction moving stage moving mechanism 50 may be configured by a linear guide, a ball screw, a radial type servo motor, in which a detection unit (for example, an encoder) for detecting the amount of movement thereof in the Z direction is built, and so on, wherein the moving stage 32 can be moved in the Z direction by driving this servo motor.
The light emitting unit 10, the mask stage 20, the projection lens 40, and the Z direction moving stage moving mechanism 50 are supported by and fixed to a single structural body (frame 60). That is, the mask stage 20 is held by the frame 60 through the frame 61 holding the mask stage, and the projection lens 40 is supported by the frame 60, which supports the entire apparatus, through the frame 62 for fixing the projection lens. Although, in the above description the drive apparatus comprises servo motors etc. as a unit for moving the work stage, a surface motor stage apparatus (for example, refer to Japanese Patent Application Publication No. 2006-149051 etc.), or a SOYA motor stage apparatus, etc. can also be used as a mechanism for moving the work stage. In addition, in FIG. 6, a control unit for controlling an operation of the exposure apparatus and a power supply unit for lighting a lamp, are omitted.
However, the above described exposure apparatus of the related art is unable to achieve a desired accuracy in the pattern formed in the workpiece, for the reasons described below.
In the exposure apparatus shown in FIG. 6, two or more workpiece marks WAM (two marks are shown in FIG. 6) are formed on a back side face of the workpiece W. Through holes 33a are formed at positions corresponding to the positions of the workpiece marks WAM of the work stage 30. And an alignment microscope 80 for detecting the workpiece marks WAM and the mask marks MAM formed on the mask M is attached to the work stage 30 through the through holes 33a. A focal point f2 of the alignment microscope 80 is set so as to be located at a top face position of the adsorption table 33, which is a position on a back side face of the workpiece W, so that the workpiece marks WAM on the back side face of workpiece W may be detected.
A procedure for exposing a workpiece comprising steps from a positioning step of the mask and workpiece to a light exposure step in the exposure apparatus of the related art will be described below.
(1) First, the mask mark MAM is detected. Exposure light is emitted from the light emitting unit 10 in a state where there is no workpiece W on the adsorption table 33. The mask mark MAM formed in the mask M is projected by the projection lens 40, and an image thereof is focused at a position corresponding to a top face of the workpiece W. A focal position f1 of the projection lens 40 (that is, a position at which an image of the mask mark MAM formed on the mask and a pattern image are focused) is adjusted in advance, so as to be located on a surface of the workpiece W when the workpiece W is placed on the adsorption table 33 of the moving stage 32.
(2) As described above, the focal position f2 of the alignment microscope 80 is located at the surface position of the adsorption table 33. Therefore, the focal position f1 of the projection lens 40 and the focal position f2 of the alignment microscope 80 do not coincide. If both do not coincide, the alignment microscope 80 cannot receive a focused and clear image of the mask mark MAM. Therefore, as shown in FIG. 7, the entire work stage 30 is raised by a distance that is equivalent to the thickness of the workpiece W by the Z direction moving stage moving mechanism 50. The focal position f1 of the projection lens 40 (an image forming position of the mask mark MAM) and the focal position f2 of the alignment microscope 80 are then in agreement with each other so that the alignment microscope 80 receives a focused image of the mask mark MAM.
(4) The alignment microscope 80 detects the projected image of the mask mark MAM, and stores the position thereof by a control unit (not shown). When the control unit stores the position of the mask mark MAM, emission of the exposure light from the light emission unit 10 is stopped. The workpiece W is conveyed by a conveyance mechanism (not shown), and is placed on the adsorption table 33 of the moving stage 32.
(5) The alignment microscope 80 next detects the workpiece marks WAM on the back side face of workpiece W through the through holes 33a of the adsorption table 33. The positions of the detected work marks WAM are compared with the positions of the saved mask marks MAM, and the control unit (not shown) moves the moving stage 32 within a plane perpendicular to the optical axis L, of the projection lens 40, in the X directions (horizontal directions on the drawing), the Y directions (front and back directions with respect to the drawing), and the θ direction (a rotation direction with respect to the optical axis), so that both mask marks MAM satisfy a predetermined positional relation (for example, the positions are match with each other).
(6) The alignment of the mask M and the workpiece W is completed by the above-described procedure, and then exposure treatment starts next. However, exposure cannot be performed in this state. This is because the focus position f1 of the projection lens 40 (an image forming position of the pattern formed on the mask M) is located at the surface position of the adsorption table 33 rather than a top face position of the workpiece W. Therefore, the work stage 30 is lowered by the thickness of the workpiece W by the Z direction moving stage moving mechanism 50 so that the focus position f1 of the projection lens 40 may be located at a surface position of the workpiece W.
(7) Exposure light is again emitted from the light emitting unit 10 in this state. An image of the pattern formed in the mask M is projected and focused on the surface of the workpiece W so that the workpiece W may be exposed. The exposed workpiece W is taken out from the adsorption table 33 by a conveyance mechanism (not shown).
As described in the procedure (6), in order to move the focus position f1 of the projection lens 40 to the front face of the workpiece W from the front face of the adsorption table 33 after positioning of the mask M with the workpiece W, the work stage 30 is moved in a direction of an optical axis L of the projection lens 40 (that is, it is lowered in the Z direction). Therefore, the straightness of the Z direction moving stage moving mechanism 50 affects the accuracy of exposure with respect to the workpiece W. As shown in FIG. 8, in the exposure apparatus shown in FIG. 6, if the straightness of the Z direction moving stage moving mechanism 50 is not good, when the work stage 30 (shown in dotted lines), which has been raised, is lowered, the moving stage 32, which holds the workpiece W, is moved within the XY plane in left-right and front-back side directions with respect to the figure (XY directions) and a rotation direction with respect to the optical axis (θ direction), so that the workpiece may shift from the position, which is aligned with the mask M.
For example, when the workpiece W is a printed circuit board, the thickness thereof is approximately 1 mm. Therefore, in the above-described procedure, the work stage 30 is moved by 1 mm in a direction of the optical axis L of the projection lens 40 (Z direction). In the case where it is moved in the Z direction by approximately 1 mm in a currently available apparatus, it turns out that a straightness deviation dxy of 0.2 to 0.3 μm is generated when in the XY direction, and a straightness deviation dθ (a shift in the XYθ direction) of 5 μrad (micro radian) is generated in the θ direction. In the above-described current apparatus, it is desired to attain an exposure accuracy of 0.5 μm or less. However, if the above mentioned shift resulting from the movement in the Z direction of such a work stage occurs, it will become difficult to attain the exposure accuracy of 0.5 μm or less.
In a conventional apparatus, the moving stage 32 having the XYθ drive unit 37 is placed on the Z direction moving stage moving mechanism 50, and the encoder provided in the XYθ drive unit 37 detects the amount of movement of the moving stage 37 with respect to the Z direction moving stage moving mechanism 50. For this reason, as described above, when the moving stage 32 is moved in the direction of the optical axis L of the projection lens 40 (the Z direction) by the Z direction moving stage moving mechanism 50, even if the moving stage 32 (adsorption table 33) holding the workpiece W is moved (shifted) in the XYθ direction because of the straightness, it is impossible to detect how much this moving stage 32 is moved in the XYθ direction.
In view of the above, it is an object of the present invention to solve the above problem. That is, it is an object of the present invention to make it possible to detect the amount of shift within a plane parallel to a workpiece face, which results from the straightness of a moving mechanism for moving a work stage in a Z direction when a work stage is moved in a direction perpendicular to the workpiece face (the Z direction), thereby adjusting the position of the workpiece.
In the work stage of the prior art, the XYθ drive unit 37, which comprises the detection unit (hereinafter also referred to as a position detection unit) such as an encoder for detecting the amount of movement in the XYθ direction of the moving stage 32, is provided on the Z direction moving stage moving mechanism 50, which moves in the Z direction. Therefore, when the moving stage 32 is moved by the Z direction moving stage moving mechanism 50 in the direction perpendicular to the workpiece face (the Z direction), the moving stage 32 and the XYθ drive unit 37 having the position detection unit for detecting the amount of movement in the XYθ direction, integrally move with the Z direction moving stage moving mechanism 50.
Therefore, even if the moving stage 32 is moved within a plane parallel to the workpiece face when moving in the Z direction (even if it shifts in the XYθ direction), the position detection unit such as an encoder of the moving stage 32, which detects the amount of relative movement with respect to the Z direction moving stage moving mechanism, cannot detect the amount of movement in the XYθ direction of the workpiece, which is produced due to straightness of the Z direction moving stage moving mechanism 50 (the amount of shift from the optical axis). For this reason, in the work stage, in which the XYθ drive unit comprising the moving stage 32 and the position detection unit for detecting the amount of movement of the moving stage 32, is provided on the Z direction moving stage moving mechanism 50, even though the positional accuracy thereof in the XYθ direction is improved, unless the straightness thereof at time of movement in a Z direction is improved, there is a limit on improvement of the positional accuracy thereof in the XYθ direction. With regards to such a problem, when the moving stage is moved in the Z direction (a direction perpendicular to a workpiece face), if the amount of shift in the XYθ direction of the moving stage can be measured, the moving stage can be returned to the original position based on the amount of shift, so that it is possible to solve the above-mentioned problem.